Abstract In refineries, due to the environmental pollutions, sulfur content in petroleum need be reduced. The incineration process is used for sulfur recovery system which is not friendly process to the environment and needs high temperature. This actual process exhaust high amount of SO 2 from the incinerator stack to the environment. The Claus process is the best method to recover sulfur from acid gases that contain hydrogen sulfide. The particular reaction for sulfur removal from sour gas is hydrogen sulfide (H 2 S) sulfur dioxide (SO 2 ) reformation (2H 2 S+O 2 =S 2 +2H 2 O). The aim of this study is to get a simulation that is suitable for the characterization of sulfur recovery units. The experimental design for this study was collected from a petroleum refinery located in Iran. This experimental relation supports us to gather with definite consistency that is normally not available online for such process. Aspen HYSYS v8.8 software was used to simulate the Claus process by reactors and component splitters. The result shows the complete conversion of sour gas to product. The simulation protects the environmental impact by SO 2 emission. This behavior can be reproduced by this HYSYS design very well. It was found that the BURNAIR feed composition and molar flow is the only factors which can affect the hydrogen sulfide conversion. The sulfur mole fraction increased only in the range of 0.94 to 0.98 by increasing N 2 from 0.7 to 0.9.